1. Field of the Invention
The invention relates to a method for producing ε-caprolactam from cyclohexanone oxime.
2. Description of the Related Art
One of the known methods for producing ε-caprolactam is to subject cyclohexanone oxime to a Beckmann rearrangement reaction in the presence of a solid catalyst. However, it is a problem of this method that the catalytic activity decreases with time due to adhesion of a so-called coke component (carbonaceous substance) to the catalyst. Consequently, in a proposed method for producing ε-caprolactam, the solid catalyst is regenerated and reused by combining the reaction process with a catalyst regeneration process for recovering the catalytic activity.
For example, Japanese Patent Application Laid-Open (JP-A) No. 53-35691 has proposed a method for producing ε-caprolactam comprising a reaction process using a boric acid catalyst supported on carbon by a fluidized bed system and a catalyst regeneration process for heat-treating the catalyst at 400 to 700° C. using air, wherein a part of the catalyst taken out of a reactor is introduced into a regenerator so that the difference of the organically-bound nitrogen content in the catalyst before and after regeneration, which is called as a differential organic nitrogen content, is maintained in a range of 0.8 to 2% by weight, and the regenerated catalyst is returned into the reactor.
JP-A No. 2000-229939 has proposed a method for producing ε-caprolactam comprising a reaction process using a solid catalyst other than the boric acid catalyst in the fluidized bed system and a catalyst regeneration process for heat-treating the catalyst at a high temperature using an oxygen-containing gas, wherein the catalyst is continuously or intermittently taken out of the reactor and introduced into a regenerator, and the nitrogen content in the regenerated catalyst is controlled in a range of 10 to 2500 ppm before returning the regenerated catalyst to the reactor.
However, since persistence of catalytic activity is not always sufficient in these conventional methods, it was a problem that the conversion of cyclohexanone oxime and selectivity of ε-caprolactam decrease during long term reactions.